Energy Sciences

Transition metal dichalcogenides have been attracting extensive attention as effective piezocatalysts for a wide range of applications, in particular, environmental remediation. Herein, WS2 nanoflowers with 2H-rich ultrathin petals are prepared by rapid synthesis based on magnetic induction heating (MIH) of sodium tungstate and thiourea, and the 2H phase is further enriched by Fe doping, in contrast to conventional pyrolysis that produces largely 1 T phase. Among the series, the sample prepared at 400 A for 10 s with an iron loading of ca. 0.1 wt% (3-Fe/WS2-400) exhibits the strongest piezoelectric response and greatest catalytic activity towards the selective reduction of oxygen to hydrogen peroxide under ultrasonic irradiation, reaching an ultrahigh H2O2 generation rate of 4.68 mM g⁻¹ h⁻¹, over 47 times higher than that of bulk-like WS₂. This is due to enhanced adsorption of O2 and manipulation of the electronic band structure by Fe doping that becomes favorable for oxygen reduction to H2O2, as manifested in theoretical studies based on density functional theory calculations. This unique property can be exploited for environmental remediation, as exemplified in the effective degradation of a range of organic pollutants. Results from this study highlight the unique potential of MIH in the structural engineering of functional nanomaterials for sustainable energy technologies.

Forming heavily-doped regions in 2D materials, like graphene, is a steppingstone to the design of emergent devices and heterostructures. Here, a selective-area approach is presented to tune the work-function and carrier density in monolayer graphene by spatially synthesizing sub-monolayer gallium beneath the 2D-solid. The localized metallic gallium is formed via precipitation from an underlying diamond-like carbon (DLC) film that is spatially implanted with gallium-ions. By controlling the interfacial precipitation process with annealing temperature, spatially precise ambipolar tuning of the graphene work-function is achieved, and the tunning effect preserved upon cooling to ambient conditions. Consequently, charge carrier densities from ≈1.8 × 10¹⁰ cm^-2 (hole-doped) to ≈7 × 10¹³ cm^-2 (electron-doped) are realized, confirmed by in situ and ex situ measurements. The theoretical studies corroborated the role of gallium at the heterointerface on charge transfer and electrostatic doping of the graphene overlayer. Specifically, sub-monolayer gallium facilitates heavy n-doping in graphene. Extending this doping strategy to other implantable elements in DLC provides a new means of exploring the physics and chemistry of highly-doped 2D materials.

Cost reduction of cell components is a major issue in PEM water electrolysis. For the anode, titanium materials with noble metal coatings represent the state of the art. For the cathode, the use of carbon-based porous transport layers, also known as gas diffusion layers (GDLs), is gaining prominence due to their significantly lower costs compared to titanium-based materials. In PEM fuel cells, carbon-based GDLs are well-established, with advancements in contact and gas/water transport achieved through micro porous layers and hydrophobic treatments. In contrast, in PEM water electrolysis, topics like interfacial contact, compression behavior, and the use of additives for carbon-based GDLs have not been widely discussed in the literature yet. With this work, we present a fundamental performance investigation of these aspects. We investigate cell performance using voltage breakdown analysis and electrochemical impedance spectroscopy, combined with subsequent Distribution of Relaxation Time analysis. Our findings highlight the effect of GDL compression and underscore the necessity of coated flow fields at the cathode. PTFE additives were found to have minimal influence on cell behavior, regardless of the presence or absence of water flow at the cathode. However, the use of micro porous layers demonstrated positive effects, particularly for ultra-low cathode catalyst loadings.

There is a growing focus on new energy sources and storage systems. The challenge with such emerging systems is their need to be warrantied for around 15 years with just a year of early testing. This requires accurate data extrapolation and estimation of the failure distribution. Physics-based approaches can be overwhelmed by the complexity of degradation, and pure data-driven approaches are inherently unable to extrapolate beyond the testing data. Here, we propose a framework for a hybrid approach for technology-agnostic customizations of a Gaussian process for stochastic and domain-knowledge-informed failure-distribution predictions. We equip the Gaussian process with customized non-stationary kernels, heteroscedastic noise models, and prior mean functions to allow for accurate extrapolation with high accuracy. Furthermore, we minimize testing time with an experiment-stopping criterion, which can significantly reduce the required data. Our framework could revolutionize energy-storage testing, enabling the rapid development of new technologies.

Thermoelectric materials are particularly relevant to the current energy infrastructure and demands of the 21st century, converting waste heat into usable electricity. The solution intercalation of zerovalent copper into Sb₂Te₃ nanoplates, a well-established thermoelectric material, is reported. The copper intercalant is homogeneously distributed throughout the nanoplates, confirmed by scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. The copper composition was shown to be 6 at. % by X-ray photoelectron spectroscopy. Copper ordering within the van der Waals gaps of the nanoplates is confirmed by selected area electron diffraction. Fabrication and thermoelectric property measurements of single-crystal Sb₂Te₃ and Cu-Sb₂Te₃ nanoplate devices show effective modulation of electrical conductivity and Seebeck coefficient with Cu intercalation. X-ray photoelectron spectroscopic studies in the valence-band region reveal additional electronic states from copper that appear near the Fermi energy, postulated to act as electron acceptors, leading to modulation of the electronic transport properties.

Magnetic materials phase reconstruction using Lorentz transmission electron microscopy (LTEM) measurements have traditionally been achieved using longstanding methods such as off-axis holography (OAH) fast-Fourier transform technique and the transport-of-intensity equation (TIE). The increase in access to processing power alongside the development of advanced algorithms have allowed for phase retrieval of nanoscale magnetic materials with greater efficacy and resolution. Specifically, reverse-mode automatic differentiation (RMAD) and the extended electron ptychography iterative engine (ePIE) are two recent developments of phase retrieval that can be applied to analyzing micro-to-nano- scale magnetic materials. This work evaluates phase retrieval using TIE, RMAD, and ePIE in simulations of Permalloy (Ni₈₀Fe₂₀) nanoscale islands, or nanomagnets. Extending beyond simulations, we demonstrate total phase retrieval and image reconstructions of a NiFe nanowire using OAH and RMAD in LTEM and ePIE in Lorentz-mode-4D scanning transmission electron microscopy experiments and determine the saturation magnetization through corroborations with micromagnetic modeling. Finally, we demonstrate the efficacy of these methods in retrieving the total phase and highlight its use in characterizing and analyzing the proximity effect of the magnetic nanostructures.

Chiral hybrid metal-halide perovskites show low-symmetry crystal structures, large Rashba splitting, spin-filtering, and strong chiroptical activity. Circular dichroism and circularly polarized photoluminescence have been investigated in chiral perovskites with increasingly distorted chiral structures. Here, we report the fabrication of chiral (R/S)-EBAPbI₃ (EBA = α-ethylbenzylamine) single crystals, which possess highly distorted octahedral structures with a high angle variance value of ∼68 degree². Using control in the fabrication conditions, we transfer chiral single crystals to thin films and achieve different crystal orientation preferences that induce tunable chiroptical properties to their heterostructures with PbI₂ nanodomains, which we characterize with in situ X-ray diffraction and grazing-incidence wide-angle X-ray scattering measurements. Using transient chiroptical spectroscopies, we resolve photoexcited charge carrier dynamics and chirality transfer processes in such heterostructures down to cryogenic temperatures. We observe rapid carrier transfer along the in-plane (002) facets in chiral perovskite phases to PbI₂ nanostructures within the initial few picoseconds, while carrier transfer along the out-of-plane (002) facets occurs at a slower rate. This fast transfer process leads to high photoluminescence intensities and large degrees of circular polarization in the emission from PbI₂ nanodomains at cryogenic temperatures. Our findings report a multidimensional chiral-achiral heterostructure which takes advantage of controllable chirality transfer and offers new routes for future spintronic and chiroptical applications.

The two-dimensional on three-dimensional (2D/3D) perovskite bilayer heterostructure can improve the stability and performance of perovskite solar cells. We show that the 2D/3D perovskite stack in a device evolves dynamically during its end-of-life decomposition. Initially phase-pure 2D interlayers can evolve differently, resulting in different device stabilities. We show that a robust 2D interlayer can be formed using mixed solvents to regulate its crystallinity and phase purity. The resulting 2D/3D devices achieved 25.9% efficiency and had good durability, retaining 91% of their initial performance after 1074 hours at 85°C using maximum power point tracking.